[OpenGL CTS] [BDW] KHR-GL45.tessellation_shader.tessellation_shader_tessellation.gl_InvocationID_PatchVerticesIn_PrimitiveID occasionally fails
Submitted by Neil Roberts
Assigned to Intel 3D Bugs Mailing List
The CTS test KHR-GL45.tessellation_shader.tessellation_shader_tessellation.gl_InvocationID_PatchVerticesIn_PrimitiveID seems to occasionally fail at a rate of about 1.4%.
The test emits a bunch of tessellation patches with varying sizes, including the maximum of 32 and does an instanced draw call. There are no vertex buffers bound and all of the vertices have the same position. The tessellation shaders write to 5 integer output varyings which are captured to a transform feedback buffer. The test then scans the buffer to verify that it has the expected values. When it fails, there are one or two vertices in this buffer that get written with all zeroes instead of the expected values. These failed slots are small and in the middle of the buffer so it doesn’t seem likely that this could be a buffer configuration issue. I suspect it might be some hardware quirk but I haven’t been able to find anything relevant in the workarounds in the hardware docs.
The hardware where I can replicate it is a NUC with Intel(R) Iris Pro 6200 (Broadwell GT3e). However I am unable to replicate it on my laptop which has Intel(R) HD Graphics 5500 (Broadwell GT2).